Aqueous dispersion of a peelable coating composition

ABSTRACT

The aqueous dispersion of a peelable coating composition of the present invention is (a) a mixture containing 5-40% by weight of an emulsion of an acrylic copolymer having a glass transition temperature (hereinafter referred to as “Tg”) of not lower than 40° C., and 95-60% by weight of an emulsion of another acrylic copolymer having a Tg ranging from −20° C. through 5° C. The acrylic copolymer emulsion mixture (b) contains ethylenically unsaturated vinyl monomers having acid value in a total amount of 0.5-1.0% by weight, and (c) at least one of the acrylic copolymer emulsions is an acrylic copolymer which has been polymerized by use of a reactive surfactant, and (d) the particle size of the acrylic copolymer emulsions is not more than 200 nm.

PRIOR APPLICATION

This application is a division of U.S. patent application Ser. No.08/953,090 filed Oct. 17, 1997, now U.S. Pat. No. 6,211,282.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an aqueous dispersion of a peelablecoating composition which is intended to be used for temporaryprotection of articles and is effective in temporary storage of articlesduring distribution, where articles may be temporarily stored in theopen air or exposed to the open air during distribution.

2. Description of the Related Art

In more and more cases, articles such as automobiles and other vehicles,machine parts, metallic household articles and other ferrous andnon-ferrous articles, wooden articles, glass articles, rubber articles,and coated rubber articles (hereinafter collectively referred to as“articles”) reach the hands of consumers after being transported fromthe manufacturer and stored temporarily in the open air. In such cases,during the period before these articles are in hands of consumers(generally this period is 2-12 months in duration), the surfaces ofthese goods are prone to becoming scratched, stained, discolored, orcontaminated due to, for example, deposits such as sandy dust, ironpowder, salts, alkalis, acids, soot and smoke, dead bodies or bodyfluids of insects, and excrement of birds and insects; sunlight; andwind and rain. Moreover, the material may come to have marks due tophysical forces.

These deposits, etc. must be removed as soon as possible, as they mayreduce the value of goods. However, removal of deposits requireselaborate work, which is accompanied by additional costs.

Thus, in order to temporarily protect surfaces of an article from beingdamaged by the aforementioned deposits, sunlight, elements, orscratches, and to eliminate the elaborate work and accompanying costs,there have been proposed a number of strippable coating compositionswhich areapplied to surfaces of an article when the article is shipped,and which, after a predetermined period of custody is over, can beeasily stripped off.

For example, two types of strippable coating compositions are used forouter panels of automobiles: one is a so-called oily wax type in whichparaffin wax is dispersed in a petroleum-based solvent, and the other isa type in which a mixture of calcium carbonate powder in paraffin wax isdispersed in a petroleum-based solvent.

These strippable coating compositions call for use of a petroleum-basedsolvent for removal, and in addition, they may raise the fear ofenvironmental problems such as air pollution. Compositions of a type inwhich an alkali-soluble resin is the primary component are also used,and these require an alkali detergent for removal, and therefore involvethe problem of environmental pollution such as water contamination.

Acccordingly, in order to eliminate the aforementioned problems, therehave been proposed emulsion-type coating compositions which form acoating film capable of being peeled off by hand after they have carriedout their function of protection (see, for example, Japanese PatentPublication (kokoku) Nos. 50-39685 and 44-29583).

However, the above-described conventional coating compositions of theemulsion type have the following drawbacks.

1) The coating compositions disclosed in Japanese Patent Publication(kokoku) No. 50-39685 are made from a single starting material.Therefore, their peeling property is not satisfactory underenvironmental conditions in which they are usually used. For example,they cannot be satisfactorily peeled off in a wide temperature rangefrom low temperatures around 5° C. to high temperatures around 40° C. atlow temperatures the formed film breaks during the peeling operation,whereas at high temperatures it stretches and thus is not quickly peeledoff.

2) Japanese Patent Publication No. 44-29593 discloses a coatingcomposition obtained through emulsion polymerization in water ofacrylonitrile and an acrylic acid ester of an lower alkyl.

Aqueous dispersions of an acrylic resin which contains acrylonitrile asan essential component raise a problem that harmful nitrogen oxides areproduced during incineration of waste films that have been peeled andcause environmental pollution.

In the meantime, regarding peelable coating compositions for use withautomobile outer panels, there exists need for compositions capable offorming a protective film that exerts contrasting functionssimultaneously in terms of adhesion; i.e., proper adhesiveness andholding power that does not permit release of the film with ease duringwater-resistance tests or that never permits release duringtransportation of vehicles under protection by the film, and ease inpeeling of the film with fingers after the period of protection by thefilm is over.

SUMMARY OF THE INVENTION

To solve the above-described problems and meet the above-stated need,the present inventors have carried out careful studies on dispersioncompositions that do not contain a nitrogen-containing vinyl monomer,and have found that an aqueous dispersion of a peelable coatingcomposition having excellent peelability can be obtained by forming an eemulsion having the following characteristics: 1) the emulsion is anacrylic copolymer emulsion which is a mixture of two acrylic copolymeremulsions, wherein the acrylic copolymers have different predeterminedglass transition temperatures, 2) the amount of ethylenicallyunsaturated monomers having acid value contained in the mixture is nothigher than a predetermined level, and 3) the emulsion does not make useof a nitrogen-containing monomer. The present invention has beenaccomplished based on this finding.

Moreover, the present inventors have found that, in addition to theabove-mentioned features 1) through 3), when 4) polymerization isperformed under conditions in which at least one of the emulsionscontains a reactive surfactant and 5) the particle size of the emulsionsis controlled to fall within a predetermined range, there can beobtained an aqueous dispersion of a peelable coating composition havingfurther improved water resistance and excellent adhesiveness, leading tocompletion of the present invention.

Accordingly, a first aqueous dispersion of a peelable coatingcomposition of the present invention is characterized by comprising

(a) a mixture containing 5-40% by weight of an emulsion of an acryliccopolymer having a glass transition temperature (hereinafter referred toas “Tg”) of not lower than 40° C., and 95-60% by weight of an emulsionof another acrylic copolymer having a Tg ranging from −20° C. through 5°C.; wherein

(b) the acrylic copolymer emulsion mixture (a) contains ethylenicallyunsaturated vinyl monomers having acid value in a total amount of lessthan 2.0% by weight; and

(c) the acrylic copolymer emulsion mixture (a) contains nonitrogen-containing vinyl monomers in the form of a monomer.

A second aqueous dispersion of a peelable coating composition of thepresent invention is characterized by, in addition to the aforementionedrequirements (a), (b), and (c),

(d) at least one of the acrylic copolymer emulsions to be incorporatedinto the mixture is an acrylic copolymer which has been polymerized byuse of a reactive surfactant, and

(e) the particle size of the acrylic copolymer emulsions is not morethan 200 nm.

MODES FOR CARRYING OUT THE INVENTION

Next will be described modes for carrying out the present invention.

A first mode of the present invention is drawn to the first aqueousdispersion of a peelable coating composition characterized by an acryliccopolymer emulsion having the below-described features (a) through (c).Synergism of these features afford, as demonstrated in Exampleshereinbelow, not only excellent physicochemical properties includingwater resistance, adhesive strength, protective power, andweatherability during the period of protection, but also excellentpeelability in a wide temperature range from low temperatures (about 5°C.) to high temperatures (about 40° C.) after the protection period isover, and in addition, when the after-use waste film is incinerated, thefilm does not generate nitrogen oxides and thus eliminates adverseeffects of environmental pollution, etc.

(a) The acrylic copolymer emulsion mixture of the present inventioncontains 5-40% by weight of an emulsion of an acrylic copolymer having aglass transition temperature of not lower than 40° C. and 95-60% byweight of an emulsion of another acrylic copolymer having a Tg rangingfrom −20° C. through 5° C.

(b) The acrylic copolymer emulsion mixture (a) contains ethylenicallyunsaturated vinyl monomers having acid value in a total amount of lessthan 2.0% by weight.

(c) The acrylic copolymer emulsion mixture (a) contains no nitrogensource such as acrylonitrile in the form of a monomer.

A second mode of the present invention is drawn to the second aqueousdispersion of a peelable coating composition of the present inventioncharacterized by, in addition to the aforementioned requirements (a),(b), and (c), the following features (d) and (e). synergism of all thesefeatures afford, as demonstrated in Examples hereinbelow, excellentphysicochemical properties including water resistance, adhesivestrength, and so on.

(d) At least one of the acrylic copolymer emulsions to be incorporatedinto the mixture is an acrylic copolymer which has been polymerized byuse of a reactive surfactant.

(e) The particle size of the acrylic copolymer emulsions is not morethan 200 nm.

Examples of the acrylic copolymer emulsion of the present inventioninclude, but are not limited to, copolymer emulsions of one or moreacrylic acid alkyl esters and/or methacrylic acid alkyl esters and oneor more vinyl monomers which are capable of being polymerized with theacrylic alkyl esters and/or methacrylic alkyl esters, wherein the vinylmonomers include vinyl acetate, hydroxyl-group-containing vinyl monomerssuch as hydroxyethyl acrylate, hydroxyethyl methacrylate,. hydroxypropylacrylate, hydroxypropyl methacrylate, and allyl alcohol,epoxy-group-containing vinyl monomers such as glycidyl acrylate andglycidyl methacrylate, and aromatic vinyl monomers such as styrene,methylstyrene, dimethylstyrene, ethylstyrene, butylstyrene, andbenzylstyrene; and copolymer emulsions of a carboxyl-group-containingvinyl monomer such as acrylic acid, methacrylic acid, itaconic acid,citraconic acid, and crotonic acid and the aforementioned one or morevinyl monomers which are capable of being polymerized with the acrylicalkyl esters and/or methacrylic alkyl esters.

It should, however, be noted that nitrogen-containing monomers includingacrylonitrile, aminoalkyl acrylates such as diethylaminoethyl acrylateand aminodimethyl acrylate, cyanoethyl acrylate, and isocyanate adductsare excluded from constituent monomers of the aforementioned acryliccopolymer emulsions.

With this exclusion, the waste coating film does not generate nitrogenoxides when incinerated, thus eliminating the fear of environmentalpollution.

According to the present invention, two acrylic copolymer emulsionshaving different Tg ranges are mixed. Specifically, the Tg range of afirst acrylic copolymer is equal to or greater than 40° C., and that ofa second acrylic copolymer is from −20° C. to 5° C.

The proportions of these two emulsions are preferably such that theacrylic copolymer emulsion having a Tg of not lower than 40° C. isbetween 5% by weight and 40% by weight inclusive and the acryliccopolymer emulsion having a Tg from −20° C. to 5° C. is between 95% byweight and 60% by weight inclusive.

More preferably, the proportions of these two emulsions are such thatthe acrylic copolymer emulsion having a Tg of not lower than 40° C. isbetween 10% by weight and 35% by weight inclusive and the acryliccopolymer emulsion having a Tg from −20° C. to 5° C. is between 90% byweight and 65% by weight inclusive.

Also, the proportion of the ethylenically unsaturated vinyl monomershaving acid value in the acrylic copolymer emulsion mixture system isnot more than 2.0% by weight, more preferably 0.2-0.8% by weight, withrespect to the weight of the entirety of the mixture.

If ethylenically unsaturated vinyl monomers having acid value arecontained in amounts in excess of 2.0% by weight, water resistance ofthe resultant coating film becomes poor, and in addition, adhesivestrength increases to render the film excessively heat- and weather-resistant and therefore the film may not be easily peeled off, which isnot preferred.

The ethylenically unsaturated vinyl monomers having acid value maybe—among those which constitute the aforementioned acrylic copolymeremulsion—carboxy-containing vinyl monomers such as acrylic acid,methacrylic acid, itaconic acid, citraconicacid, and crotonic acid. However, the ethylenically unsaturated vinyl monomers having acid value arenot limited only to these compounds.

In the present invention, examples of the reactive surfactants include“Aqualon RN” series (tradename, Dai-ichi Kogyo Seiyaku K.K.) which aresurfactants of the polyoxyethylene alkylphenyl ether type in which aradical-polymerizable propenyl group has been introduced into thehydrophobic group; anionic surfactants, “Aqualon HS” series (tradename,Dai-ichi Kogyo Seiyaku K.K.) which are based on the sulfuric ester saltsof “Aqualon RN”; acrylic anion surfactants, “Eleminol RS30” and“Eleminol JS-2” (tradenames, both by Sanyo Chemical Industries, Ltd.)and “Adeka Reasoap” series (trade name, Asahi Denka Kogyo K.K.).

When reactive surfactants are added upon synthesis of acrylic copolymeremulsions, water resistance of the coating film is improved, filmstrength is enhanced, and peelability of the film is promoted.

The particle size of the acrylic copolymer emulsions is preferably notmore than 200 nm, more preferably not more than 100 nm. When theparticle size is in excess of 200 nm, a sufficient contact area cannotbe obtained between the composition and the surface of the object to becoated, which leads to poor water resistance.

The aforementioned mixture may incorporate, as desired, small amounts ofadditives which may be useful in the manufacture of peelable-coatingcompositions. Such additives include plasticizers (e.g., phthalateesters and fatty acid esters), wax emulsions (includingpolyethylene-based emulsions and polypropylene-based emulsions),defoaming agents (e.g., mineral oils and silicone oils), Rheologymodifier (including inorganic type and organic type), UV absorbents(e.g., benzotriazoles and benzophenones), pH modifiers (e.g., organicalkalis and ethanolamines), preservatives (e.g., benzoisothiazolines andtriazines), coalescing agents (e.g., alkyl ethers of mono- ordi-ethylene glycol and alkyl ethers of mono- or di-propylene glycol),anti-freezing agents (e.g., polyhydric alcohols), peelability-improvingagents (e.g., silicone emulsions and alkylphosphoric esters), dryingaccelerators (e.g., lower alcohols such as ethyl alcohol).

The peelable coating composition of the present invention is intended tobe applied onto surfaces of articles such as automobiles and othervehicles, machine parts, metallic household articles and other ferrousand non-ferrous articles, wooden articles, glass articles, rubberarticles, and coated rubber articles, to thereby protect the surfaces ofthe articles in the open air or indoors. Needless to say, thecomposition of the present invention may be used for protecting surfacesof objects other than the above articles.

Specifically, the aqueous dispersion of peelable coating composition ofthe present invention is advantageously used, for example, for thefollowing purposes.

1) Prevention of stains and scratches, or degradation due to UV rays,etc. of panel coatings and resin portions of automobiles.

2) Prevention of rust stains of machine parts.

3) Prevention of stains of edible oil and dirt from hands, when appliedto ventilation fans and kitchen devices and utensils,

4) Prevention of stains and scratches of aluminum fences.

5) Prevention of stains and scratches of indoor floors.

6) Protection of the wall or floor materials in a paint booth againstsplashing of paints.

7) Prevention of scratches, or maintenance of good appearance whenapplied to skis made of an FRP resin.

EXAMPLES

The present invention will next be described by way of Examples whichdemonstrate the effects of the invention as contrasted to ComparativeExamples. However, the present invention should not be construed asbeing limited by the examples.

The emulsions having Tgs and particle sizes as shown in Tables 1 through3 below were prepared, and subjected to the tests described hereinbelow.

The glass transition temperature (Tg) of each composition was measuredin accordance with JIS K7121 “Testing Methods for TransitionTemperatures of Plastics”

TABLE 1 1) Acrylic copolymer emulsion having a Tg of 40° C. or more TgParticle Ethylenically unsaturated (° C.) size (nm) Surfactant monomerhaving acid value (wt %) A1 58 80 Reactive 0.6 A2 58 80 Non-reactive 0B1 46 75 Reactive 0.8 B2 46 75 Reactive 5.0 C 46 250 Reactive 0.5 D 46100 Non-reactive 0.1

TABLE 2 2) Acrylic copolymer emulsion having a Tg from −20° C. to 5° C.Tg Particle Ethylenically unsaturated (° C.) size (nm) Surfactantmonomer having acid value (wt %) F1 2 85 Reactlve 0.4 F2 2 85 Reactive 0G 2 300 Reactive 0.5 H 2 250 Non-reactive 0.7 I −15 80 Reactive 0.7

TABLE 3 3) Acrylic copolymer emulsion having a Tg from 5° C. to 40° C.Tg Particle Ethylenically unsaturated (° C.) size (nm) Surfactantmonomer having acid value (wt %) E 15 80 Reactive 0.5

4) Method for Emulsion Polymerization

<Emulsion A1>

In a glass reactor equipped with a reflux condenser, a stirrer, athermometer, a dropping funnel, and a gas-introduction tube were chargedammonium persulfate (1.25 parts), water (250 parts), a reactivesurfactant “Aqualon RN-20” (trade name, Dai-ichi Kogyo Seiyaku K.K.)(1.8 parts), methyl methacrylate (MMA) (25 parts), butyl acrylate (BA)(23 parts), acrylic acid (AA) (2.3 parts), and t-dodecylmercaptane (0.9parts). While the contents of the reactor were stirred, the air in thereactor was purged with nitrogen gas, and subsequently, the reactor washeated in a water bath (maintained at 60° C.).

When the temperature of the mixture in the reactor reached 60° C., amonomer mixture consisting of “Aqualon RN-20” (8.2 parts), methylmethacrylate (MMA) (112.5 parts), butyl acrylate (BA) (102 parts),acrylic acid (AA) (10.2 parts), and t-dodecylmercaptane (3.9 parts) and2 wt. % aqueous sodium hydrogensulfite solution (32 parts) were addeddropwise respectively for two hours.

After completion of addition, the system was stirred for 2 hours at 60°C.

After completion of reaction,the mixture was cooled to obtain athermoplastic resin emulsion containing 48% solids and having a pH of3.2.

This system was neutralized with ammonia water to thereby obtain astable emulsion A1. The Tg of this emulsion as measured in accordancewith JIS K7121 was 58° C., and the average particle size was 80 nm.

<Emulsions B1, B2, C, E, F1, F2, G, I>

In a manner similar to that employed for emulsion A1, Emulsions B1, B2,C, E, F1, F2, G, and I were prepared by changing the proportions of themonomers and changing the amounts of surfactants, to thereby obtainemulsions B1, B2, C, E, F1, F2, G, and I, having different particlesizes.

<Emulsions A2, D, and H>

In the case of emulsions A2, D, and H in which a nonreactive surfactantwas used, a surfactant (trade name “Triton X-301,” Rohm & Haas), aninitiator, and water were charged from the first, and when thetemperature of the mixture reached 60° C., a monomer mixture and aterminator were added to thereby obtain an emulsion A2, D, or H.

Through use of emulsions A1 through I, the following compositions, i.e.,representatives of the present invention and the comparative examples,were obtained.

Composition (unit: part(s) by weight) Emulsion D 35 Emulsion H 63Defoaming agent 0.4 Rheology modifier 0.1 pH modifier 1.5 MFT (minimumfilm-forming temperature) = 12° C. Ethylenically unsaturated monomerhaving acid value  : 0.49% by weight

Example 2

Composition (unit: part(s) by weight) Emulsion C 37 Emulsion G 59Defoaming aqent 0.5 Rheology modifier 0.1 Peelability-improving agent1.0 pH modifier 1.4 Coalescing agent 1.0 MFT = 5° C. Ethylenicallyunsaturated monomer having acid value  : 0.50% by weight

Example 3

Composition (unit: part(s) by weight) Emulsion D 35 Emulsion F 63Defoaming agent 0.4 Rheology modifier 0.1 pH modifier 1.5 MFT = 12° C.Ethylenically unsaturated monomer having acid value  : 0.16% by weight

Example 4

Composition (unit: part(s) by weight) Emulsion A2 30 Emulsion F2 67Defoaming agent 0.5 Rheology modifier 0.1 Peelability-improving agent1.0 pH modifier 1.4 MFT = 12° C. Ethylenically unsaturated monomerhaving acid value  0% by weight

Example 5

Composition (unit: part(s) by weight) Emulsion B2 37 Emulsion F2 60Defoaming agent 0.4 Rheology modifier 0.1 pH modifier 1.5 Coalescingagent 1.0 MFT = 10° C. Ethylenically unsaturated monomer having acidvalue  : 1.94% by weight

Example 6

Composition (unit: part(s) by weight) Emulsion A 30 Emulsion I 68Defoaming agent 0.4 Rheology modifier 0.1 pH modifier 1.5 MFT <0° C.Ethylenically unsaturated monomer having acid value  : 0.67% by weight

Example 7

Composition (unit: part(s) by weight) Emulsion B 37 Emulsion I 60Defoaming agent 0.5 Rheology modifier 0.1 Peelability-improving agent1.0 pH mddifier 1.4 MFT <0° C. Ethylenically unsaturated monomer havingacid value  : 0.74% by weight

Example 8

Composition (unit: part(s) by weight) Emulsion B 25 Emulsion F 73Defoaming agent 0.4 Rheology modifier 0.1 pH modifier 1.0Peelability-improving agent 0.5 MFT = 7° C. Ethylenically unsaturatedmonomer having acid value  : 0.35% by weight

Composition (unit: part(s) by weight) Emulsion D 20 Emulsion I 77Defoaming agent 0.5 Rheology modifier 0.1 Peelability-improving agent1.0 pH modifier 1.4 MFT <0° C. Ethylenically unsaturated monomer havingacid value  : 0.58% by weight

Comparative Example 1

Composition (unit: part(s) by weight) Emulsion A 48 Emulsion F 48Defoaming agent 0.4 Rheology modifier 0.1 pH modifier 1.5 Coalescingagent 2.0 MFT (minimum film-forming temperature) = 10° C. Ethylenicallyunsaturated monomer having acid value  : 0.50% by weight

Comparative Example 2

Composition (unit: part(s) by weight) Emulsion B2 36 Emulsion F 59Defoaming agent 0.4 Rheology modifier 0.1 pH modifier 1.5 Coalescingagent 2.0 MFT (minimum film-forming temperature) <0° C. Ethylenicallyunsaturated monomer having acid value  : 2.34% by weight

Comparative Example 3

Composition (unit: part(s) by weight) Emulsion E 98 (Tg : 15° C.)Defoaming agent 0.4 Rheology modifier 0.1 pH modifier 1.5 MFT (minimumfilm-forming temperature) = 12° C. Ethylenically unsaturated monomerhaving acid value  : 0.5% by weight

Test Items and Methods

<Preparation of Test Specimens>

The specimens used in the tests were coated plates prepared as follows.Electrodeposited mild steel plates were spray-coated with an aminoalkydresin-base paint. When the surface drys to Touch, an acrylic resin-baseclear paint was sprayed, and the plates were subsequently baked at 140°C. for 20 minutes. To the resultant painted plates were applied each ofthe compositions prepared in the above-described Examples andComparative Examples so as to have a film thickness of 70 μm (dry). Adiversified tests were performed in terms of the below-describedproperties by use of the thus-prepared coated plates as test specimens.

* Peelability: Peelability of test specimens placed at 5° C., 25° C., or40° C. was checked.

* Acid resistance: A droplet of 40% sulfuric acid aq.soln was placed oneach test specimen, and the specimen was allowed to stand for 15 minutesin a 60° C. thermostatic chamber.

After the specimen was cooled to room temperature, the film was peeledoff, and changes of the paint were checked.

* Alkali resistance: A droplet of 0.1N sodium hydroxide aq.soln.wasplaced on each test specimen, and the specimen was allowed to stand for3 hours at 70° C. After the specimen was cooled to room temperature, thefilm was peeled off, and changes of the paint were checked.

* Water resistance: The film-coated test specimens were soaked in 25° C.water for 24 hours, and the whitening degree was observed.

* Adhesive strength: The film-coated test specimens were soaked in 25°C. water for 24 hours, and presence or absence of natural peeling-offwas observed.

* Peelability after heated: The test specimens were left in a 80° C.thermostatic chamber for 500 hours and subsequently peelability waschecked at room temperature.

* Accelerated weather resistance: The test specimens were placed in anSWOM tester for 500 hours so as to accelerate degradation of the filmand subsequently peelability was checked.

* Cycle test: Each test specimen was subjected to a cycle test, in whicheach cycle consisted of heating at 80° C. for 24 hours and subsequentcooling at 0° C. for 24 hours. After the test specimen had undergone 10cycles, peelability of the specimen was checked.

* External exposure: The test specimens were exposed to the open air inOkinawa prefecture. When six months (including 3 months in summer) hadpassed, peelability of the specimen was checked.

* Combustion test: A small amount of film that had peeled off wascollected and burned. Nitrogen oxides contained in the combustion gaswere analyzed in accordance with JIS K0104.

The test results are shown in Table 4.

The evaluation standards were as follows:

A: Very good, B: Good, C: Poor, and D: Very poor.

TABLE 4 Test Results Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 A Peelability AB A A A A B Acid resistance B A A A A A C Alkali resistance B A A A A AD Water resistance B B B B A A E Adhesive strength B A B B A A FPeelability after heated A B A B A A G Accelerated weather resistance AB B B A A H Cycle test B A B B A A I External exposure B A B B A A JCombustion test A A A A A A MFT (° C.) 12 5 12 12 10 <0 Ethylenicallyunsaturated 0.49 0.5 0.16 0 1.94 0.67 monomers having acid valueEmulsion particle size 100/250 250/300 100/85 80/85 75/85 80/80Surfactant N/N R/R N/R N/R R/R R/R Test Results Comp. Ex. Comp. Ex Comp.Ex Ex. 7 Ex. 8 Ex. 9 1 2 3 A Peelability A A A D D D B Acid resistance AA A A B A C Alkali resistance A A A A D A D Water resistance A A A A B AE Adhesive strength A A A A B A F Peelability after heated A A A C D C GAccelerated weather resistance A A A C D D H Cycle test A A A D D C IExternal exposure A A A D D B J Combustion test A A A A A A MFT (° C.)<0 7 <0 10 <0 12 Ethylenically unsaturated 0.74 0.35 0.58 0.5 2.34 0.5monomers having acid value Emulsion particle size 75/85 75/85 100/8080/85 75/85 80 Surfactant R/R R/R N/R R/R R/R R/R A: Very good B: GoodC: Poor D: Very poor N: Non-reactive surfactant R: Reactive surfactant

As shown in Table 4, whereas specimens falling within the scope of thepresent invention were excellent with respect to all the test items,those of comparative examples were inferior to the specimens of theinvention, proving the synergism achieved by the present invention.

As described hereinabove by way of examples, the aqueous dispersion ofpeelable coating composition of the present invention which is anacrylic copolymer emulsion exhibits excellent peelability due to thesynergism of the following features: 1) The composition comprises amixture of two acrylic copolymer emulsions, wherein the acryliccopolymers have different predetermined glass transition temperatures,2) the amount of ethylenically unsaturated monomers having acid value inthe mixture is not higher than a predetermined level, and 3) theemulsion does not make use of a nitrogen-containing monomer.

Moreover, in addition to the above-mentioned features 1) through 3),when 4) polymerization is performed under conditions in which at leastone of the emulsions contains a reactive surfactant and 5) the particlesize of the emulsions is controlled to fall within a predeterminedrange, there can be obtained, as a result of further synergism, anaqueous dispersion of a peelable coating composition having furtherimproved water resistance, adhesiveness, and peelability.

Furthermore, since no nitrogen-containing monomers such as acrylonitrileare contained in the acrylic emulsions, when the film is peeled offafter the protection period is over and the waste film is burned anddisposed of, gases containing nitrogen oxides are not generated and thusthere is no fear of environmental pollution.

Accordingly, the aqueous dispersion of peelable coating composition ofthe present invention enables to achieve protective effects superior tothose obtained from previous products when used, for example, for thefollowing purposes.

1) Prevention of stains and scratches, or degradation due to UV rays,etc. of panel coatings and resin portions of automobiles.

2) Prevention of rust stains of machine parts.

3) Prevention of stains of edible oil and dirt from hands, throughapplication to ventilation fans and kitchen devices and utensils,

4) Prevention of stains and scratches of aluminum fences.

5) Prevention of stains and scratches of indoor floors.

6) Protection of the wall or floor materials in a paint booth againstsplashing of paints.

7) Prevention of scratches, or maintenance of good appearance whenapplied to skis made of an FRP resin.

What is claimed is:
 1. A peelable film on a substrate to be protectedwherein said film is made from a liquid composition consistingessentially of (a) a mixture containing 5-40% by weight of an emulsionof an acrylic copolymer having a glass transition temperature(hereinafter referred to as “Tg”) of not lower than 40° C., and 95-60%by weight of an emulsion of another acrylic copolymer having a Tgranging from −20° C. through 5° C.; wherein (b) the acrylic copolymeremulsion mixture (a) contains ethylenically unsaturated vinyl monomershaving acid value in a total amount of less than 0.2-2.0% by weight; and(c) the acrylic copolymer emulsion mixture (a) contains no constituentmonomers having nitrogen.
 2. The peelable film of claim 1 wherein atleast one of the acrylic copolymer emulsions described in (a) is anacrylic copolymer which has been polymerized by use of a reactivesurfactant, and the particle size of the acrylic copolymer emulsions isnot more than 200 nm.
 3. The peelable film of claim 1 wherein thesubstrate to be protected are portions of the exterior of an automobile.4. A method of protecting a substrate comprising applying to thesubstrate an aqueous dispersion consisting essentially of (a) a mixturecontaining 5-40% by weight of an emulsion of an acrylic copolymer havinga glass transition temperature (hereinafter referred to as “Tg”) of notlower than 40° C., and 95-60% by weight of an emulsion of anotheracrylic copolymer having a Tg ranging from −20° C. through 5° C.;wherein (b) the acrylic copolymer emulsion mixture (a) containsethylenically unsaturated vinyl monomers having acid value in a totalamount of less than 0.2-2.0% by weight; and (c) the acrylic copolymeremulsion mixture (a) contains no constituent monomers having nitrogenand drying the same to form a peelable film.
 5. A method of protecting asubstrate, according to claim 6, comprising applying to the substrate anaqueous dispersion wherein at least one of the acrylic copolymeremulsions described in (a) is an acrylic copolymer which has beenpolymerized by use of a reactive surfactant, and the particle size ofthe acrylic copolymer emulsions is not more than 200 nm and drying thesame to form a peelable film.
 6. The method of claim 4 wherein thesubstrate is an exterior panel of an automobile.